1. Field of the Invention
The present invention relates to an exposure-scanning apparatus for focusing an erect, equal-sized light image of an original document on an image-receiving sheet.
2. Description of the Prior Art
Exposure-scanning apparatuses are used in electrophotographic printing machines of the direct-exposure type. These machines reproduce original documents on image-receiving sheets having a photoconductive surface such as photosensitive paper, without using image-transmitting elements such as photoconductive drums or belts.
In direct-exposure type electrophotographic printing machines, the photoconductive surface of an image-receiving sheet is charged by a charging device. Then, a charged photoconductive surface is exposed to an erect, equal-sized light image of an original document by means of the exposure-scanning apparatus, thereby forming an electrostatic latent image. After exposure, the electrostatic latent image is developed by a developing unit, and then, a developed image is fixed on the image-receiving sheet. This image-receiving sheet, may then be used as a master plate for an offset printing machine.
In the conventional exposure-scanning method for focusing an erect, equal-sized light image of an original document on an image-receiving sheet, use has been made of an optical exposure system comprising a combination of a focusing optical transmission body, such as a bundle of focusing optical fibers, and a light-reflecting mirror having an odd number of reflecting surfaces. Here, the original document and the image-receiving sheet are moved in opposite directions relative to and parallel with the optical exposure system. This means that if the original document is maintained stationary, the optical exposure system would have to be moved at one given speed and the image-receiving sheet would have to be moved in the same direction at a speed twice that of the optical exposure system.
Based on this principle, there have been proposed exposure-scanning appratuses wherein the original document and the image-receiving sheet are moved in opposite directions while the optical exposure system is maintained stationary, and exposure-scanning apparatuses wherein the original document is maintained stationary and the optical exposure system and image-receiving sheet are moved in the same direction.
A direct-exposure type electrophotographic machine adopting the former type of exposure-scanning apparatus is disclosed in, for example, Japanese Examined Patent Publication (Kokoku) No. 56-39468. The former type of apparatus, however, suffers from problems in the timing of movement of the original document and the image-receiving sheet and deviation of the center axis of the original document from that of the image-receiving sheet.
A direct-exposure type electrophotographic machine adopting the latter type of exposure-scanning apparatus is disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 53-56208. In the latter type of apparatus, the image-receiving sheet is placed on an endless belt and moved in the same direction as that of the optical exposure system at twice the speed. Accordingly, the unstable position of the image-receiving sheet on the belt, frequently results in floating or misalignment of the sheet during exposure and scanning.